Photolithography, sometimes referred to as optical lithography or UV lithography, is a process used to pattern films or substrates in semiconductor or integrated circuit (IC) manufacturing. Lithographic photomasks are typically transparent fused silica blanks covered with a pattern defined by a light absorbing or reflecting film. A set of photomasks, each defining a pattern layer, is fed into a photolithography stepper or scanner, and individually selected for exposure. Light passes through the photomasks and hits, typically, a layer of photoresist on the substrate in the pattern of the photomask. Various chemical treatments may be used to remove the exposed portions of the photoresist (or the un-exposed portions, in a negative resist). When using photolithography for mass production of IC devices, the typical term for a photomask is photoreticle or reticle. Fabrication of some IC devices may require more than 50 exposures using different reticles.